Colour specification

ABSTRACT

There is disclosed a method for preparing a colour chart comprising the steps of defining a reference colour, specifying a range of colours from said reference colour, each colour being spaced by integral multiples of a preselected colour difference value from any other colour, the range spanning the colour space between the reference colour and some other colour.

[0001] This invention relates to colour charts.

[0002] Colour charts are prepared by manufacturers of paints, inks,dyestuffs and coloured products as diverse as motor vehicles and sewingthreads. Usually, they are published as printed colours, laid out insome sort of array, on paper, but swatch cards are also produced by, forexample, manufacturers of fabrics, laminates and so forth in which thecolours are shown on the fabric or laminate itself. The colours areselected in accordance with the preferences of an individual or panel ofpeople, perhaps after some market research, and assigned more or lessfanciful names such as Nile Green or Dusky Peach. Disclaimers are oftenmade as to the reproducibility of the chart colours, especially inregard to the differences brought about by application to the intendedsubstrate as compared with the chart colour on its paper substrate.

[0003] Some colour charts, comprehensive enough to be termed ‘colourlibraries’ are necessarily arranged in some kind of logical order. Amongthese may be mentioned the CIELAB colour model, and the Pantone, ScottDic and Munsell systems. At least one of these libraries has beentransferred from the physical samples to an electronic version in whichthe colours are stored as brightness, hue and chroma values fordisplaying a colour on a colour monitor. A problem with electronicrepresentation, of course, can be appreciated by casual observation oftelevision sets in a dealer's window—not all the sets will be showingthe same colour, despite receiving the same signal.

[0004] A shortfall of all of these systems is that by no means allavailable colours are represented. Even though, typically, there may besome 1700 colours in such a library, manufacturers are not infrequentlyasked for ‘specials’, colours not represented by chart colours.

[0005] The present invention provides methods for preparing colourcharts, colour charts prepared by such methods and apparatus fordisplaying colour charts and colours therefrom that do not suffer thedisadvantages of prior art charts and their display and which haveconsiderable advantages to those concerned with the specification orproduction of colour and coloured articles.

[0006] The invention comprises, in one aspect, a method for preparing acolour chart comprising the steps of

[0007] defining a reference colour, and

[0008] specifying a range of colours from said reference colour, eachcolour being spaced by integral multiples of a preselected colourdifference value from any other colour, the range spanning the colourspace between the reference colour and some other colour

[0009] Typical colour difference values are CMC values. The preselectedcolour difference value may be at least one CMC value and may desirablybe in the region of two CMC values.

[0010] A CMC value (as specified by the Colour Management Committee) isa trade-wide adopted standard for colour differentiation. It is definedas the difference, in CIE colour space, comprising differences in hue,chroma and lightness, between a specified and an achieved colour, asspecified by the CMC formula. It renders numeric measures of colourdifference which are generally accepted as being visually uniform i.e.the same magnitude of CMC value is the same colour differenceirrespective of the colour.

[0011] Whilst it is possible to contemplate charts for green, red orother subsets of the entire gamut of colour, the invention is mostmeaningful when the whole gamut is covered. The reference colour, then,may be the deepest possible black, or the purest and brightest possiblewhite.

[0012] This method of specifying colours fills the colour spaceextending from deepest black to brightest white, and encompassing red,green, yellow and blue, with approximately 17000 colours. There islittle or no point in specifying finer differences than are commerciallyonly just distinguishable. The number is larger—far larger than anyother commercial colour chart—but manageable. Because of the structureof the chart, it lends itself to an orderly, objective, rather thansubjective, identification of the colours. While many systems could bedevised, a straightforward, easily understandable system is to labeleach colour with an alphanumeric code of the form AA123. The potentialrange of available code numbers is 676000, which is far larger than isrequired for the 17000 or so colours of the full chart, so there isperhaps, room for interpolation, should it for any reason be desired toadd further colours. On this basis, jet black could be represented asAA000 and whitest white by ZA000.

[0013] The invention also comprises a colour chart comprising a range ofcolours specified for a defined reference colour each colour beingspaced by integral multiples of a preselected colour difference valuefrom any other colour, the range spanning the colour space between thereference colour and some other colour. The reference colours may bewhite, black, or, indeed any other colour and the range may comprisethose colours in the colour space which are spaced from an adjacentcolour by at least one CMC value, preferably by about two CMC values,e.g. 1.8 or 2.2 CMC values.

[0014] Of course, it would not be possible to make any meaningful colourchart for the whole of colour space on a single sheet of paper. Rather,sub-ranges can be indicated, using the labelling method outlined above,by the alpha part of the code on a segment of a circular colour map, andthe chart proper can be on a page-by-page basis for colours representedby codes beginning AA, AB, AC, . . . BA, BB, BC, . . . ZA, ZY, ZZ.

[0015] Obviously, such a “chart” could run to 676 pages, and might beunmanageable for many purposes. The chart can, however, be representeddigitally for display via a programmed computer on a colour monitor, andthe invention also comprises apparatus for displaying a colour chart,comprising

[0016] a colour video monitor, and

[0017] a computer programmed to specify a range of colours extendingfrom a defined reference colour each colour being spaced by integralmultiples of a predetermined colour difference value from any othercolour, the range spanning the colour space between the reference colourand some other colour

[0018] the computer being connected to the monitor and controllable todisplay at least one colour of the range thereon.

[0019] Having regard to the problems of displaying colours alluded toabove, it is preferred that the monitor is calibratable, both internallyto itself and externally to the computer, so that the colour actuallydisplayed corresponds to the specified colour. The monitor can becalibrated with reference to standard colours by means of a colorimeter.Rather than resort to the usual colour adjustments available on colourmonitors, it may be that the colour signals sent between the computerand the monitor are adjusted (the adjustments being, for example, storedin a database which is consulted each time a colour signal istransmitted) by means of a feedback from the colorimeter.

[0020] In much the same way, a colour printer can be calibrated to printcolours which match the screen colours or a set of standard colours.

[0021] While the measures described above can be used to produce acolour chart and to display its colours accurately on screen or printedon to paper, there remains the problem of producing the finishedproduct, be it a textile product, a ceramic, a leather, a laminate orwhatever, which involves the production of an appropriate colorant whichit will perfom on the substrate to which is will be applied. Textiledyestuffs, for example, will yield different colours on differentsubstrates, for example, substrates having different textures. Thisproblem can also be addressed in conjunction with the invention.

[0022] In another aspect, then, the invention comprises apparatus asaforesaid in which the computer contains a database of colour recipesfrom which a particular recipe is desired representative of a colourdisplayed on the monitor which will produce the actual colour whenapplied to a particular substrate. The database will contain differentrecipes for the same colour but for application to different substrates.The recipes may be in digital format which, for a perfect screen, woulddisplay the called-for colour, and the machine contain programmingmodifying the instructions to the screen (or printer, as the case maybe) to produce the colour called for. The programming may include analgorithm, which will be a method of working out a recipe for examplefor paints, inks and/or dyes. The computer, in other words, may includeprogramming adapted to modify the instructions on the basis of adifferent substrate, as outlined above.

[0023] The invention will now be described with reference to thedrawings, in which:

[0024]FIG. 1 is a colour map such as might be used in connection withthe invention;

[0025]FIG. 2 is of an example of a page of colours from a colour indexprepared according to the invention; and

[0026]FIG. 3 is a diagrammatic illustration of apparatus useful inconnection with the preparation and display of colours in a colour chartaccording to the invention.

[0027] The drawings illustrate a method for preparing a colour chart 11comprising the steps of

[0028] defining a reference colour, eg black (AA000, FIG. 1) or white(ZA000, FIG. 1) and

[0029] specifying a range of colours from said reference colour (AA000or ZA000), each colour being spaced by integral multiples of apreselected colour difference value from any other colour, the rangespanning the colour space between the reference colours and some othercolour.

[0030] The colour difference values are CMC values.

[0031]FIG. 1 illustrates the coding system. The first letter of the codeis an indication of lightness, A being dark, Z being bright, a letterlate in the alphabet indicating a lighter colour than a letter earlierin the alphabet.

[0032] The lightness/darkness spectrum is depicted in planes A, B, . . .Y, Z.

[0033] The second letter denotes to chroma circle, A denoting the“bull's eye”, B, D . . . Z denoting the first, second etc circlesoutside this, a letter later in the alphabet denoting a less intenseshade than one earlier in the alphabet.

[0034] The first numeric digit denotes which of the four quadrants thecolour appears in, quadrant 1 extending from red to yellow (therebyencompassing orange shades) quadrant 2 extending from yellow to green,quadrant three from green to blue, and quadrant 4 from blue, throughpurples, back to red.

[0035] The next two digits represent the distance around the colourcircle from the beginning of the quadrant. Thus 126 represents thetwenty sixth point around the first quadrant, thus a reddish orangecolour. The full coding BD126 thus represents a point on circle D in thesecond lightness plane, 26 points around the circle from the beginningof quadrant 1, thus a dark, intense reddish orange colour.

[0036] With a little experience, any colour denoted by this coding inthe form xxnnn can be fairly readily visualised.

[0037]FIG. 2 shows a typical page from a compendium of all colours of acolour chart according to the invention. The page, selected, as it were,at random from all the pages labelled AA to ZA, is page EC and contains25 colours, EC100, EC108, EC106, . . . EC192. EC196. Other pages will besimilar. Of course, other configurations can be adopted. The pages canbe pages of a paper publication or pages' of text and graphics in acomputer.

[0038] Of course, different coding systems can be adopted, but the oneparticularly herein described appears well suited for adoption as astandard.

[0039]FIG. 3 illustrates apparatus for displaying a colour chartcomprising a colour video monitor 31 and a computer 32 programmed tospecify a range of colours between to reference colours each colourbeing spaced by an integral multiple of two CMC values from any othercolour, the range: spanning the colour space between the two referencecolours, and the computer 32 being connected to the monitor andcontrollable to display at least one colour of the range thereon.

[0040] A colour printer 33 is also connected to the computer 32—inasmuchas a printer is essentially a printing VDU, although not so fast inresponse nor so flexible in operation as a VDU—the colour printer 33 isauxiliary to the video monitor 31. Provision for internal calibration isdesirable so that it may be ensured that signals passed to the monitoror printer from the computer always result in the same colour beingdisplayed or printed.

[0041] Likewise, adjustment may be made for changes in the appearance ofa colour when it is applied to different substrates. This may be doneexactly as described, namely by comparing the screen or printed imagewith a colour on a particular substrate, or the effect of colorants suchas dyestuffs on different substrates such as woven or knitted fabrics,fabrics which have and fabrics which have not been bleached, and so on,can be taken into consideration in a database loaded into the computerand consulted when a dye recipe, for example, for dyeing onto ecrucotton fabric is required.

1. A method for preparing a colour chart comprising the steps ofdefining a reference colour specifying a range of colours from saidreference colour, each colour being spaced by integral multiples of apreselected colour difference value from any other colour, the rangespanning the colour space between the reference colour and some othercolour.
 2. A method according to claim 1, in which the reference colouris black.
 3. A method according to claim 1 or claim 2, in which thereference colour is white.
 4. A method according to any one of claims 1to 3, in which the preselected colour difference value is at least oneCMC value.
 5. A method according to claim 4, in which the preselectedcolour difference value is between 1.8 and 2.2. CMC values.
 6. A colourchart comprising a range of colours specified for a defined referencecolour each colour being spaced by integral multiples of a preselectedcolour difference value from any other colour, the range spanning thecolour space between the reference colour and some other colour.
 7. Acolour chart according to claim 6, in which one of the reference coloursis black.
 8. A colour chart according to claim 7 or claim 8, in whichone of the reference colours is white.
 9. A colour chart according toany one of claims 6 to 8, in which the range of colours comprises thosecolours in the colour space, which are spaced from an adjacent colour,by at least one CMC value.
 10. A colour chart according to claim 9, inwhich the colours are spaced by between 1.8 and 2.2 CMC values.
 11. Acolour chart according to any one of claims 6 to 10, representeddigitally.
 12. Apparatus for displaying a colour chart, comprising acolour video monitor a computer programmed to specify a range of coloursextending from a defined reference colour each colour being spaced byintegral multiples of a predetermined colour difference value from anyother colour, the range spanning the colour space between the referencecolour and some other colour the computer being connected to the monitorand controllable to display at least one colour of the range thereon 13.Apparatus according to claim 12, in which the monitor is calibratable.14. Apparatus according to claim 13, in which the monitor is internallycalibratable.
 15. Apparatus according to claim 13 or claim 14, in whichthe monitor is externally calibratable.
 16. Apparatus according to anyone of claims 13 to 15, comprising a colour printer.
 17. Apparatusaccording to claim 17, in which the printer is calibratable. 18.Apparatus according to any one claims 13 to 17, in which the computercontains a database of colour recipes from which a particular recipe isselectable representative of a colour displayed on the monitor, whichwill reproduce the actual colour when applied to a particular substrate.19. Apparatus according to claim 18, in which the database containsdifferent recipes for the same colour but for application to differentsubstrates.
 20. Apparatus according to claim 18 or claim 19, in whichthe recipes are in digital format which, for a perfect screen, woulddisplay the colour called for, the machine containing programmingmodifying the instructions to the screen (or printer, as the case maybe) to produce the colour called for.
 21. Apparatus according to any oneof claims 18 to 20, in which the programming includes an algorithm,which is a method of working out a recipe for paints, inks and/or dyes.